Variable-capacity air compressor



`une 14, 1927.

B. v.. NoRDBl-:RG

VARIABLE CAPACITY AR vCOMPUSSSOR Filled sept. 8, 1925 2 sheets-smvu @Hoeft/m35 June 14, 1927. 1,632,498

B. V. NORDBERG VARIABLE -CAPACITY AIR COMPRESSOR @Lf/mung* K j Patented I Junevv 14, i,

I moitoy Vgl RDBERG, OFMLWAUKEE, WisCoNs1N; HELENA c.u :toitiiiairisiinriifrir-` j rmx or sAin BRUNO Vbnonn'nne, DEcnAsnn.

' VAiiIABnn-onracirramfooiirnnsson. y

. ApplicationlledSeptember8,11923; SerialiNo; 661,649.

a This iiiventioniielates to variable "capacity jf coiiipressoi's and particularly :toth'at type in 'f f which the capacity/ofthe compressor is l'inirxfed hyf Varyingtlie point. of cut-off of aninletyaive so as tol vary the Weight oi'v gas :drawnfiiito thezcylinder ateacli lWorking stroke.v n v i ln a ,prior f -Patent, No.v` 900,418,granted tonie Octoher, 1908,1 describe a iii-echa- "nismoikthisgeneral! type in vwhich a drop font-oli' yalyegearis iised toncontrol oscili `lating",inlet Valves yto effect the desiredfiiiicf `the inlet Valve double-ported, as isthe case inV largeaiid infast running compressors,-

tion.

vIn my present disclosiire,as `in inyafprior' .patent above identified, l; illustrate 'a valve -g'ear forming the' subject matter of Patent iim'portant. v l

reasonfthat such yalye gearv is vsiniple and.; vsatistactory and "is capable orv giving a cut-V off at any point'in thefworking stroke. `It should he noted, howeyenthat any Valve gear The'airangeinent,disclosed inJinyPatent y against.` outflow from the. cylinder: '-thiough infcasesr Where a' single-ported inlet Valve' is used; When itbecornes `necessary tor make seinedfhciilty is encoiinteredffor theyreason (that ythefi'iilet lvalize'iniist be -qiiiteflarge in r diameter and niiist he Vprovided with `packing strips oriothervineansto keep itgtight. This problem isfleoinplicated 4vloyljthe Vlfact that` when j the compressor isriinningbelow ifiillJ capacity there is al portiony offthestrole in which the' supply pressure predoini'nates o'verieyliiider.pressureso that the packing oi'theinletvvalve must seal against pressures `gactiirg alternately innreyerse'directions.k Y

` Afterithelinlet'valye' cuts off or closes,r the tureA is lowered.Tk :In lthe ensuing compression stroke,` the :temperature :again :rises vas the compression progressesk and if; .there kWere no lossfor gain offflieat loyi the" air, its temperature vwould be equal to tliatoi the inlet air at the point, Where the `coinairain the cylinder expands and itsftemperaf y iii which* long as "non a'ir` leaks into the [cylinder during `the .f period of i reduced pressure. If, lioweventhereshould he such a leak,

f'tliegi: temperatiire Woiildi not he loweredy sui# f icientlyvduring the .time s the cylinder Ipresvl .siire-alllsbelowsupply pressure,-` and this opeddiiriiigptlieensiiingcoinpression period. VVhen-the `compressorWorks loWfvlca- `-joacitythe'gratio of compression' may he Very y `lii'ghwso tliat'it is obvious thats-ii addition yoiheat totlieair `at or near the beginning vofthe compression strokey would result iii 'V .-fqiiite a `high.te'iiipeiature at the ,end of )coin-Y` pressionf ;Hence,y tight; sealing oi `thein-let 7 `both directions is vitally? l K 1 0. g

obviously tendsfto increase the heatudeve valve nieclianisni in n In .its broad aspects,` the present invention eonteniplatesthe addition to -a Vcompressor havingeithergaiitoinatic or positivelynactii atedinlet yalvesofyariable cut-ofi inlet'controlling valves placed the ``inletports,-` seat-v The 'main or ordinary inletfiyaly'e's seal the inlet ports,- andthe, variable ciit-oiffvalyes are opeiiitliroiighoiit the lentire suction stroke,

75 i `ing in the direction oiinletilow; and acting` Elto ciitoiyai'ialily the inlet ilow.; In, its iia'r s n .reiter aspects, the invention yinyolves Various details: hereinafter' fully discussed.v

Vsealagainstthe 7inflow of air froiii theysiipi yplyjto the cylinder.` The 'mainv inlet. valves S5 asare the-drop cnt-oil Valves-When the 'coins 4pressoir 4operates Lat; iii-ll eapa'cityf When the drop ciitfoi yalvesf close at ypart stroke, they aresiibjected to aAv preponderating `supply pressure. Thus leakage is preyentediirhoth Adirections andA since eachnvalve seals against :pressure only' in one f direction, the Valvesv can yhe simply constructedandrcanibe made Very free act-ing.

z. f Theconstriiction outlined permits the apk.plication of the broad Vinventive*principles` I oif iny Patent,No. 900,418,to largefand fast.; Lriinning compressors.

. A.; preferred `ieinloodiinent of theV .invention is1illiistrated" in" the f.aeconipaiiyin'g-- drawings,

loo

Fig. l is a Vieivgpart'ly in section andpartly 3 in side eleyation, showing the? invention as applied toa fdouble.acting.cylinder` having f positivelyactu-ated niaiii 'inlet'. valves and xaiitoniaticdischarge `Valves; f f

Fig. 2 is a fragmentary section through the cylinder of Fig. 1, showing the valves ot the head-end working space;

Fig. 8 is a view similar to Fig. 2 showing automatic in lieu oi positively actuated main inlet valves;

Fig. il is a view similar to Fig. 3 showing how an automatic inlet valve and a variable eut-oft1 inlet valve may be closely mounted to reduce the intervening port volume; and

Fig. is a diagram representing a typical theoretical indicator card for compressors ol. the constructions illustrated in Figs. 1 to 4 when the cut-off valve closes at about half stroke.

Referring first to Figs. 1 and 2, l shall describe those parts which are essentially similar to corresponding parts illustrated in Patent No. 900,11-18.

The engine frame is illustrated at 11, the crank shait at 12, the cylinder at 13, and the wrist plate at 111. rlhis wrist plate is illustrated as of the bell-crank type, and is provided with two arms for directly actuating the valve gear hereinafter described. The piston 1G is reciprocated in the cylinder 13 by means of the usual piston rod 17, which is connected through a connecting rod and crank (not shown) to the crank shaft 12 in the usual manner. The piston rod 17 is provided with a tail rod or extension 18 as is common in the art.

Mounted on the crank shaft 12, at approximately 90O from the crank, is the main valve actuating eccentric 19, whose strap 20 is connected through the rod 21, rocker 22, and rod 23 to the wrist plate 1st. A second eccentric 2el, angularly displaced from the main eccentric 19, is also mounted on the crank shaft 12, its strap 25 being connected by the rod 26, rocker 27, and rod 28, to oscil late a pendant link 29, fulcrumed at 80 on the trame 11.

The pressure regulator' is essentially identical with that illustrated in Fig. 1- ot Patent No. 900,118 and, so tar as is material to the present invention, may be described as including a vertically slidable sleeve 31, which is urged upward by air pressure in the discharge chest ot the compressor, and which is urged downward by a weight The weight 32 is made in sections so that the discharge pressure against which the compresser is to work may be adjusted. The sleeve 81 is formed with a groove 83 at its upper end which is engaged by a pivoted fork.A not shown, positively connected with the arm 84. The arm 31 is iulerumed at and hence is swung upward by an increase in discharge pressure and allowed to tall by a decrease.

The arm 8i is connected by links 3G and 8T. which are pivoted together to the horizontal arm 38 ot a three-armed lever whose other two arms 39 and a0 are connected to the trip cams hereinafter described. The pivotal connection between the links and 37 is O'uided by a short arm '11, also tulcrumcd at 30. but movable independently of the pendant link 29.

The three-armed lever just mentioned is pivoted at on the lower end ot the peudant link 29, consequently, when the compressor is running, the link 29 and, with it, the three-armed lever is oscillated about the pivot 30 by the eccentric 2i. The rise and iall oi the sleeve 31 merely rocks the threearmed lever on the t'ulcrum -12. Since the arm 39 projects upward from the arm 38, and the arm L10 downward, and since the trip cams are reversely arranged as hereinafter mentioned.I the movements oi the sleeve 31 alicet both trip cams equally and in the same sense.

Referring now to Fig. 2, the discharge valves will he described with reference to that used at the head end of the cylinder. Any desired type olt discharge valve might be used, but I have chosen for illustration an automatic valve ot the reed type, in which a plurality of thin resilient reeds i3 are mounted over the apertures in grids Lil. These grids are i'formed in a unitary cylindrical plug or insert f1-5, which is inserted in an opening in the cylinder head and which is retained therein by a removable bonnet 40 (see Fig. 1).

rl`he main inlet valve i? shown as :1n ordinary double-ported valve of the Corliss or oscillating type. 1t is positively actuated in the usual manner b v an arm i8 fixed on its stem and connected by a link L19 with one arm 15 or" the wrist phi e. .l similar, but reversely arranged, valve is used at the crank end oi the cjv'linder. These main inlet valves 1T are timed to remain open throughout the suction stroke and they are so mounted that they are held to their seats by cylinder pressure when this prcpondeates over inlet pressure.

Mounted as close io the inlet side oi' cach main inlet valve `l? as is po. ible is a second double-ported valve :10, ot' the oscillating .or Corliss type, which is so arranged as to be urged to its seat when the pressure ol" supply predominates. This valve is chosen as typical ot the class oi variable cut-oil valves and` in tact. l prefer lt'or this` duty a valve oi' the drop cut-oli' type. lt may be actuated b f an),v valve gear which will give a range oi variable cut-olil cocxtensive with the stroke. For this purpose I illustrate the valve gear described in my two prior patents and hence need describe it ouhv generally.

The valve closing arm 51 is tast on the stem ot the valve 50, and is urged in a valve closing direction by a plunger in the dash pot 52 connected by the rod 53 with the arm 5l. rihe valve opening arm 5i is .mbuntedf io. ecilifelicaiaiiyf wifir die.; lvalve .50 andwisconnected by a link 'wvitlr y thefarin:4.8ofthe;correspondingniain inlet f' block 58 Whiclijcoactslin the/usual manner Uwith a `latch block: on lthe va'lve closing f arm.y 'The trip arm 56de provided with. a;

coursefixedgin place andthe valve: opening* arm '543 `which actuates thevalve 50,` is con- Y nected directly to an ariii lliotheywrist f;

Crank pin `60 `which gages in the V*trip cani [groove 61.l `The groovejlgisf formed in a cam` plate 62 pivoted fatonthe'rvalvejopenf f. ing :armv and. ."oscillates4 .thereoiii through-av link flNn-QfjQTlii's k'link 64 lis"'coniiected Vto fthe corresponding one of `the arms Sil-e0 of the three-armed lever. 1 Consequently, the. trip cams 6l are oscillatedfby"theteccentric 24 under the control` of `r"they governor "sleeve j"Ihe .valve "501is so timed asto` lose :at

the .end ioit-i the "suction strolez; i. e., simul- `"taiieously .Withfthevalve ,Whenever the i -compressor is VWoiflring atiiill .capaeity.

"Under kthis conditionthe latch isnot tripped* by. `the y trip cam. `l/Vhen the 4compressori Works atrediicedrcapacity; the valve 50de@ :lo f; .lleld. @0 its. Seafby .inltpfseille :During "the compression stroke@ both valvesiaiey tripped y-closedxJvhile the.. valve 47:- remains `cylinder pressureto.v dropbeletv` Vthe pressure yof supply and rconsequently tlieyalve 50 is The possibility@ iinieifigiiie igwfo waives* litogether,A assliowntinlig.fhJ arisesufrom the fact thaitheiw i p undei'fthe,conditioiisof iillstroke operafjY o` valves` tiined Itogether As suggestedit p `lpossibleltosubstitute automatic valves forthe mechanieally operated inlet valvesf. gFig. `3 `shows asiinple manner of inodiif'yingthe structure of Fig. V2

, changed and for thefvalve 47 reed valves 172.- This valveA to vtl'iis end. The'portoformation is slightly p is substituted" a .cylindrical plug ,'Ofhaving-grids .71,V aiidjf isyessentially identicalr with the discharge valve structure alrefaclv described and like kthe l.dischare i .valveo-peniiig arnisj are connected directly7 valve, isu held in place `by a bonnet. The plug' 'lofcourseis listed in posit-ion. Consequei'it-V lv7 the roc-keriarins 48 are omitted andthe to the Wrist platen` instead ot :indirectly through connection Withrthe arm Syasrin Fig. 1.o.' This change involves a diilerentiiiro npoi'tioningok-ofthe, linkage to vsecure the proper timing of the valve 50, but thisis a matter ofdesign, Which Will be obvious to those skilled in? the-art.` v.

Onek diliiculty y which encountered the `use of autoinaticinletvalves is clearly illustrated in ligzj.v This is thelarge port volume between the' reed valves 72fand'tlie "drop cut-off valve 50 Wliiclilpiodiices avai-.- iableclearance space' and henceafects they Y A y yoilyalve50 closes.4 open.V Y The I closing ofthje valvez' 50 causes' operationpf the .conipressorgfvThestriic tureilliistrated in Fig. Qhas afniuclisinallei' Mkport volume interveningbetiveen the valves. In Fig; 4l, Ishow a rearrangement ofthe structure of Fig. 3, in which fthe gridsl'] 47e 'i and reed valves 72 are formediiia relatively"o large plug 73, which is further provided with a ported "seat to receive the drop-cutoff valve 50. The Plug' inthis'construction is ofj l .platea-fs described iiic'onnectionQiritlilig; The' diagram billig. vshovvsoa -thei'eti-p` cahcard' Whencut-oilbyjvalve 50 occurs at k89 aboutinid-strole.. Air entersfjftlie compressor at a pressure P1 andis dischargedat a higher pressure P2.` At the beginning of thev siiction stroleat'i, vthe inletfvalves are "Closedl and' theicylinder pressure is 132.g'l`vlie1` air .expandsback'toy the inlet pressure ll v,andi

reaches that pressureat ZJ, at Whichpoint the at pressure?1 tothe point Herethgeoiiti' `The volume at@l is the i v clearance, incliiding` the port if'oliinie to'Y the jdro'p lcut-off valve 50, Atthe vend,otfthe siictionA stroke `the pressure in the cylinder has 1 Vdropped gto vsome. reduced. pressure "Sinceftlieinletival efcloses at dtherolui o iindergoiiig` compression is the piston dis' let valve, andsuchrclearance-*is `li The compression, i up to: the point e,- Atakes place `While vthe'pressure' in tliecydinder Volume do plus th e et d.; During the espansione/d,thereis Y partialwjaeuuin inzthe cylinder andlealiafge i losA placement plus. the olearzincel to tlieniainfinthank the-elearan'ce to the variable clit-oil valve 50.*

below the inlet pressure P1. f During this peiiodtlie )cuteolf valve 50 continues to seal againstythe entrance of air; the main suction valve being ineffectiveforothisfiunotionbef` p $115.

cause it seats only` under preponderatin cyliiider pressure. `f

' Since the expansion from o to l takes placeWith a `larger clearance than the `coiiipression lfroin (Z to e, the compression pressure rises faster. lThis makesv the volume e greater than the volume "b lcas shown.`

`Thetshaded area c d e in thediagramsivillff i therefore represent workdone-by the coin` pressor. The volumeeje and` hence Ithevf i '125 less according to the Vport 'volurrievbetweeii".

the main inlet valve and `the variable cutfoff shaded areafjust mentioned7 is greater or valvei 50. I prefer the positively actuated*` -V type of main cut-off valve,vshown Figsgl and 2, forthe reason that suchintervening port volume can be made very small With this type oit valve.

From c compression continues to at which point pressure P2 is attained in the cylinder. The discharge valve then opens and discharge occurs along the line 7' a, at pressure P2.

The volume drawn into ldie compressor under the cenditions described is equal to e and the work necessary to compress it is represented by the area (l, c (Z e j.

vWhat is claimed is:

1. The combination ot a compressor having inlet and discharge valves; a variable eut-ott valve arranged to be held to its seat by inlet pressure and to control the fionY ot gas through the inlet valve; and means for varying the point or" cut ott ot' said cut-oil valve.

2. The combination of a compressor having an inlet valve, the latter being arranged to be held to its seat by prepouderating cylinder pressure; a variable cut-oil1 valve arranged to be held to its seat by preponderating supply pressure and to control the tio-vv through said inlet valve; and means for varying the point ot cut oil ot said cut-ott valve.

3. The combination of a compressor having an inlet valve arranged to be held to its seat. by preponderating cylinder pressure; a variable cut-oill valve situated on the inlet side ot said inlet valve and arranged to control the iow thereto and to be held to its seat by preponderating supply pressure; and means for varying the point ot cut-ofin ot said cut-olil valve.

il. The combination of a compressor having an inlet valve arranged to be held to its seat by preponderating cylinder pressure; a variable cut-oill valve situated on the inlet side of said inlet valve and arranged to control the flow thereto and to be held to its seatby preponderating supply pressure; and pressure controlled automatic means tor varying the point of eutoif ot' said cut-oil valve.

5. The combination ot a compressor having an inlet valve of the mechanically actuated type; an inwardly seated variable cutotl valve arranged to control flow through said inlet valve; mechanical means serving normally to actuate said valves in unison; and a pressure regulator operable by the rise ot discharge pressure above normal and servingl to advance the closing ot said cutoil' valve relatively to said inlet valve.

The combination ot' a compressor having an inlet valve of the mechanically actuated type; a cut-oli' valve arranged to control the tlovv through said inlet valve; mechanical means tor actuating said valves substantially in unison; a releasing and closing mechanism serving to release said cutol' valve from said actuating means and cause it to cutoll in advance olt the closing oit said inlet valve; and pressure controlled means serving to vary the point ot such cut oil'.

7. The combination ot a compressor having an inlet valve or the mechanically actu` ated type; a reversely seated cut-oil' valve also controlling the inlet, and situated close to and in advance ol the inlet valve; mechanical means for actuating said valves substantially in unison; a drop cut-oil mechanism arranged to close said cut-oil' valve in advance ot the closing of said inlet valve; and pressure controlled means serving.r to vary the point ot action ol said drop cut-olil mechanism.

t5. The combination of a compressor having an inlet valve of the mechanically actuated oscillating type; a reversclv seated cutolf valve ot the oscillating type also controlling the inlet and situated close to and in advance ot the inlet. valve; a variable drop cut-ott mechanism ior said cut-ott' valve operable at substantially any point in the Working stroke; actuating means arranged to operate said valves substantially l in unison; and pressure controlled means operatively related to said drop cut-oil mechanism and serving to advance variably the point of cut-oit ol the cut-oli valve.

In testimony whereof l have signed mv name to this specification.

BRUNO V. NORDBERG. 

